Enantiomerically pure binaphthol has found use as important constituents of asymmetric reagents used in organic synthesis. Optically active binaphthol has been used, for example, as chiral auxiliary in the preparation of chiral catalysts for asymmetric hydrogenation; the preparation of chiral crown ethers for use as stereoselective complexing agents; and the preparation of organotitanium reagents and hydroboration catalysts. Further, such optically pure binaphthol may be useful in asymmetric synthesis of chiral polymers such as polyesters, polyphenylene oxides and polyethers. Similarly, optically active spirobiindanol has found use in the preparation of chiral polycarbonates.
The acquisition of such useful optically active compounds has relied chiefly on the resolution of racemic (R,S)-.+-.-1,1'-bi-2-naphthol and (R,S)-.+-.-spirobiindanol as the asymmetric synthesis of such compounds involves complex multistep synthetic routes.
For example, the (R)-(+)- and (S)-(-)-1,1'-bi-2-naphthol enantiomers have been obtained by first preparing diastereomeric cinchonine salt derivatives of phosphate esters of racemic binaphthol which salts are then separated by fractional crystallization and reduced and recrystallized to produce separated (R)-(+)- and (S)-(-)-1,1'-bi-2-naphthol.
In similar manner, the (R)-(+)- and (S)-(-)enantiomers of spirobiindane acids have been obtained, for example, by preparing diastereomeric derivatives of the racemate which are then separated by fractional crystallization, reduced and recrystallized to provide optically active isomers.
Such traditional chemical methods of enantiomeric separation, however, have presented problems in the preparation of optically active isomers on a synthetic scale as such methods are tedious and expensive. In particular, the chiral derivatizing agents used to prepare diastereomers are both expensive and difficult to reuse and the separation of diastereomeric derivatives by fractional crystallization can lead to process scale up problems, for example, in the preparation of enantiomers on a synthetic scale.
HPLC methods using columns packed with chiral stationary phase have also been used for separation of enantiomers. However, such methods are typically analytical techniques and can also be difficult and expensive to scale up and perform on a synthetic scale.
In view of that above, a definite need therefore exists for a convenient and economical method for separating the enantiomers of racemic binaphthol and spirobiidanol which can be performed on a synthetic scale.
Recently, several methods of applying enzymes to organic synthesis which overcome the aforementioned disadvantages associated with traditional chemical methodology have been used in the separation of enantiomers on a synthetic scale. For instance, methods of stereoselective hydrolysis of various ester compounds by use of an esterase to obtain optically active compounds or to create chiral compounds from prochiral compounds are known. Examples of such methods include U.S. Pat. No. 4,588,694 wherein the production of optically active (S)-(+)-3-alkyl-5-acyloxymethyl-oxazolidin-2-one derivatives via esterase catalyzed asymmetric hydrolysis of corresponding racemic esters is reported; Japanese Pat. Application No. 6224439 wherein the biochemical production of (R)-4-hydroxy-2cyclopentanone from asymmetric hydrolysis of racemic 4-hydroxy-2-cyclopentanone-organic carboxylic acid ester in the presence of an esterase; and Japanese Pat. Application No. 61092596 wherein the production of optically active indoline-2-carboxylicacid is provided by esterase catalyzed asymmetric hydrolysis of (R,S)-indoline-2carboxylic acid ester.
Other examples of optically active compounds prepared by esterase catalyzed asymmetric hydrolysis are described in U.S. Pat. No. 4,731,476 (esterase catalyzed stereoselective hydrolysis of L-Leucine ester to optically pure L-Leucine); European Pat. Application No. 243167 (description of a novel esterase useful in the economic production of optically active compounds via asymmetric hydrolysis and the creation of chiral compounds from prochiral compounds); Japanese Pat. Application No. 62205042 (treatment of racemic d,1-cyclopentanone esters with esterase to effect asymmetric hydrolysis to optically active substances); Japanese Pat. Application No. 62129238 (esterase catalyzed asymmetric hydrolysis of cyclopentanone esters to optically active cyclopentanone derivatives); Japanese Pat. Application No. 61173788 (preparation of 4-chloro-3-hydroxybutyric acid by esterase catalyzed asymmetric hydrolysis of the corresponding acid ester); Japanese Pat. Application No. 61104797 (preparation of optically active 1-(4-phenoxyphenoxy)-propane-2-ol via esterase catalyzed asymmetric hydrolysis); Japanese Pat. Application No. 59118737 (stereoselective hydrolysis of d-4-cyclopentanone esters by porcine liver esterase, bovine liver esterase, lipase and the like); and Japanese Pat. Application 57193495 (preparation of optically active furanyl carboxylic acid esters via stereoselective esterase hydrolysis). See also, Ladner, et al., 106 J. Am. Chem. Soc. 7250-1 (1984) (resolution of enantiomerically pure epoxy alcohols by asymmetric lipase catalyzed hydrolysis of epoxy alcohol esters); Findeis, et al., 19 Annu. Rep. Med. Chem. 263 (1984) (enantiospecific hydrolysis of racemic threo esters with pig liver esterase to the (-)-acid); and Iriuchijma, et al., 46 Agric. Biol. Chem. 1907 (1982) (resolution of racemic imidazolone to (+)-biotin via stereoselective esterase hydrolysis). For further examples, see Laumen, et al., 26 Tetrahedron Lett. 407-410 (1985); Schneider, et al., 23 Angew. Chem. Int. Ed. Engl. 64-66 (1984); and Wang, et al., 106 J. Am. Chem. Soc. 3695 (1984).
In view of the above, it is therefore an object of the present invention to provide a novel and simple method for preparing optically active binaphthol and spirobiindanol from respective racemates on a synthetic scale. It is a further object of this invention to provide such a method wherein said optically active compounds are conveniently prepared from the enzyme catalyzed stereoselective hydrolysis of corresponding racemic esters.